Apple Motion 4 - Manual (Page 523)

3 If you’d like, modify the color and opacity of the stars.
For more information on modifying shapes, see Shape Parameters .
4 In the Layers tab, double-click the group that contains the stars, type “Stars” in the text
field, then press Return.
The group is renamed Stars.
5 Apply the Gravity behavior to the Stars group.
Gravity behavior applied
to group (not to
individual layers of the
group)
The animation path created by the Gravity behavior appears in the Canvas, and the group
of stars falls when you play the project. Because the behavior is applied to the group, all
layers in the group fall at the same rate.
6 To increase the rate of the falling layer, drag the Acceleration slider in the Gravity HUD
or Inspector toward the right (this example uses an Acceleration value of 100).
Note: You can enter a negative number in the Acceleration value field in the Inspector
to make the layer float upward rather than fall.
To use the Edge Collision behavior
1 Apply the Edge Collision behavior to the Stars group.
523 Chapter 9 Using Behaviors